The present invention relates to the field of firefighting and more specifically to the field of firefighting utilizing aerated foam via a foam chamber as a fire suppressant in storage environments. For example, when a flammable liquid is stored in a tank it is common for regulations to require that a fixed fire protection system be provided and situated above the stored liquid level. Such fire protection may take the form of a fire suppressant fluid that is aerated in a foam chamber to produce a foam discharged at the top of a storage container or tank, the fire suppressant fluid being supplied by a supply line to a foam chamber where air or inert gas is mixed as the fluid expands within the foam chamber.
The basic design of foam chambers is controlled by Underwriter's Laboratory Standard 162, the Standard of Safety for Foam Equipment and Liquid Concentrates. This standard sets forth certain requirements for foam chamber design, the main requirements being a means to aerate foam solution into a viable fire fighting foam and a means to prevent flammable or combustible vapor from escaping from the tank by use of a frangible vapor seal. This frangible vapor seal is required to withstand pressure at the inlet to the foam chamber of a least 7 psi, but is required to rupture before reaching a maximum inlet pressure of 25 psi.
Following the Standard 162, many foam chamber designs share several features including: a flow control means, an aeration means, a secondary expansion means, a tertiary expansion means, a discharge means, a vapor seal, and a means to gain access to the interior of the foam chamber.
With respect to the flow control means, many foam chambers utilize either an orifice plate or a flow nozzle to control the flow rate at a given inlet pressure.
Many foam chambers currently available that apply an aeration means utilize an internal device to break up the stream of fire suppressant flowing through the inlet orifice or the nozzle, depending on which is used, so that the fluid spreads to fill an inlet conduit thereby entraining air that enters through a series of openings in the inlet conduit and expands the solution with air to a volume about equal to two times the solution volume and reduce the velocity by approximately 30-40% and reducing the pressure inside the conduit thereby resulting in a partially aerated foam.
Many prior art foam chambers utilize a conduit approximately two times the cross section area of the inlet conduit to further reduce the velocity of the expanding aerated solution to approximately 30-40% of the solution inlet velocity, again reducing the pressure inside the conduit resulting in higher expansion.
Tertiary expansion means found in many foam chambers in the prior art utilize a third conduit or expansion enclosure for a final expansion phase with the third conduit being approximately four to five times the cross section of the secondary expansion means thus resulting in a further drop in velocity and internal pressure, and development of a final expanded fire fighting foam.
It is common in the prior art for foam chambers to utilize a fourth conduit as a discharge means, usually approximately three to four times the cross section of the first aeration means conduit. The discharge from this conduit is directed to the interior of the flammable liquid storage tank where a device known as a deflector directs the discharge so that it flows down the inside wall of the flammable liquid storage tank where it is gently applied to the surface of the burning flammable liquid.
Vapor seals utilized in many foam chambers currently available can be divided into two basic types. The first type, and most common, is a vapor seal located at the outlet of the secondary expansion means conduit. The most common material used for vapor seals when located at this point is glass that has been scored or possibly otherwise altered to control the breaking pressure. The second type, and least used, is to use a vapor seal located at the discharge from the tertiary expansion means.
Many prior art foam chambers currently available utilize a removable access means, usually consisting of a plate or a hatch that is bolted, screwed, or otherwise removably attached to the top end of the tertiary expansion means. Because of the design of the prior art, this access means must be removed any time the foam chamber is to be tested, and with most existing foam chambers having the vapor seal at the discharge of the secondary expansion conduit, an additional discharge device must be installed to direct the foam discharge away from the tertiary expansion conduit to prevent its entering the protected tank through the discharge means conduit. If the vapor seal is located at the entrance of the discharge means conduit, expanded foam is prevented from entering the tank, however, the foam chamber access means must be left open for testing.
In the course of utilizing a foam chamber fire suppressant system, it sometimes becomes necessary to test various components of the system to ensure safe and reliable function. As described above, testing of foam discharge and the frangible seal of a foam chamber can be difficult if not impossible under the prior art. None of the basic designs described above, covering all known present designs, allow easy testing of foam discharge from the foam chamber without opening of the access means and applying an additional device, and allow no method for testing the vapor seals after foam chambers are placed in active service. Thus there exists a need in the art for a foam chamber that allows for quick and clean testing of both the foam chamber functionality and of the frangible vapor seal without risking contamination of the storage container or tank contents.